The present invention relates generally to a new and novel method of induction hardening heat treated gear teeth. More particularly, the present invention relates to a new and novel method of induction hardening heat treated gear teeth which provides a final gear having both a tough ductile core, as well as high residual compressive stresses in the root of the gear teeth.
In the field of gear manufacturing, it has long been desirable to produce a gear which has a tough ductile core, while at the same time having high residual compressive stresses present in the root of the gear teeth. One known prior attempt to fabricate such a gear includes the steps of rough cutting the gear teeth, carburizing, but not hardening the gear teeth, finish cutting the gear teeth and then induction hardening the entire gear tooth. While finish cutting the gear teeth after carburizing may result in a gear having improved dimensional characteristics, the cost of such a gear would be prohibitive.
A preferred embodiment of the present invention is, therefore, directed to induction hardening of heat treated gear teeth which includes the steps of rough and finish cutting the gear teeth, or alternatively cutting the gear teeth to their final configuration utilizing a one cut method, carburizing the gear and in particular, the gear teeth, slow cooling, or alternatively drawing back, the gear so the gear teeth are not hard and induction hardening the gear teeth heating only the surface of the gear teeth. This results in improved strength for the gear teeth as a result of increased residual compressive stresses therein. Induction heating of only the surface of the gear teeth results in a relatively shallow case depth in the root of the gear teeth. Since the residual compressive stresses increase as the case depth decreases, the fatigue life of such a gear will be improved as compared to gears produced using known prior art methods which utilize the case depth from the carburizing process which results in a relatively deeper case and, therefore, lower residual compressive stresses in the gear teeth and a less than desirable fatigue life.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawing.